Non-invasive or in vivo interrogation of biological tissues with light waves is becoming increasingly important in medicine. Some of the techniques employed are diffuse-reflectance spectroscopy, fluorescence measurement, imaging etc. In various applications for taking measurements from biological tissues, the targeted tissues tend to be under the skin as subsurface tissues such as the fluorescence-based detection of cancerous tissues. Specifically, testing glucose levels based on blood tests requires measurements of blood samples by first obtaining blood samples and then conducting measurements of obtained the blood samples. Many conventional glucose testing techniques based on measuring blood samples use a lancing device to actuate a lancet to cut a target skin location such as a patient's fingertip to obtain a small amount of blood for blood testing and to measure the blood glucose level. This and other blood testing methods require cutting of the skin and thus are invasive.